Electrochemical cells, such as miniature alkaline air cells, are stable, high-energy sources for electrical devices such as hearing aids. An alkaline electrolyte must be sealed within the confines of a miniature alkaline air cell to prevent corrosive damage to the exterior of the cell and possibly to the electrical device in which it is housed, while a continuous supply of air must be provided to the surface of the air electrode.
Generally, a miniature alkaline air cell comprises an outer metal container having at least one air opening in its base to provide air to the active air electrode, a hydrophobic film layer, an air electrode, a separator layer, an anode mask, and an electrolyte. The cell assembly is capped with a gasket and metal cell cover which seals the open end of the cell container thereby sealing in the alkaline electrolyte. The term "gasket" as used herein refers to a non-ventable sealing member for providing a fluid-tight joint between battery components. Gaskets for alkaline air cells have generally been made from nylon, polypropylene or polysulphone, with nylon being preferred, especially nylon 66. However, nylon gaskets for miniature alkaline air cells have major disadvantages. First, nylon absorbs moisture making it susceptible to hydrolytic degradation in a corrosive electrolyte. As a result of the tendency for nylon to absorb moisture, it must be dried prior to molding. After molding, the dimensions and properties of the resulting nylon gasket are affected by the tendency of nylon to absorb moisture. Hydrolytic degradation of nylon occurs through chain scission of amide bonds. Chain scission embrittles the nylon gasket making it susceptible to stress cracking, which leads to gasket failure and leakage of electrolyte from the cell.